Darzynkiewicz Z, Traganos F, Sharpless T, Melamed M R
J Cell Biol. 1976 Jan;68(1):1-10. doi: 10.1083/jcb.68.1.1.
Heat denaturation profiles of rat thymus DNA, in intact cells, reveal the presence of two main DNA fractions differing in sensitivities to heat. The thermosensitive DNA fraction shows certain properties similar to those of free DNA: its stability to heat is decreased by alcohols and is increased in the presence of the divalent cations Ca2+, Mn2+, or Mg2+ at concentrations of 0.1-1.0 mM. Unlike free DNA, however, this fraction denatures over a wide range of temperature, and is heterogeneous, consisting of at least two subfractions with different melting points. The thermoresistant DNA fraction shows lowered stability to heat in the presence of Ca2+, Mn2+, or Mg2+ and increased stability in the presence of alcohols. It denatures within a relatively narrow range of temperature, consists of at least three subfractions, and, most likely, represents DNA masked by histones. The effect of Ca2+, Mn2+, or Mg2+ in lowering the melting point of the thermoresistant DNA fraction is seen at cation concentrations comparable to those required to maintain gross chromatin structure in cell nuclei or to support superhelical DNA conformation in isolated chromatin (0.5-1.0 mM). It is probable that factors involved in the maintenance of gross chromatin organization in situ and/or related to DNA superhelicity also have a role in modulating DNA-histone interactions, and that DNA-protein interactions as revealed by conventional methods using isolated chromatin may be different from those revealed when gross chromatin morphology remains intact.
完整细胞中大鼠胸腺DNA的热变性曲线显示，存在两种对热敏感性不同的主要DNA组分。热敏性DNA组分表现出某些与游离DNA相似的特性：醇类会降低其对热的稳定性，而在浓度为0.1 - 1.0 mM的二价阳离子Ca2 +、Mn2 +或Mg2 +存在时，其稳定性会增加。然而，与游离DNA不同的是，该组分在很宽的温度范围内变性，并且是异质的，由至少两个具有不同熔点的亚组分组成。热抗性DNA组分在Ca2 +、Mn2 +或Mg2 +存在时对热的稳定性降低，而在醇类存在时稳定性增加。它在相对较窄的温度范围内变性，由至少三个亚组分组成，并且很可能代表被组蛋白掩盖的DNA。在与维持细胞核中总体染色质结构或支持分离染色质中超螺旋DNA构象所需的阳离子浓度相当的情况下（0.5 - 1.0 mM），可以观察到Ca2 +、Mn2 +或Mg2 +对降低热抗性DNA组分熔点的作用。可能参与原位维持总体染色质组织和/或与DNA超螺旋相关的因素也在调节DNA - 组蛋白相互作用中起作用，并且使用分离染色质的传统方法所揭示的DNA - 蛋白质相互作用可能与总体染色质形态保持完整时所揭示的不同。
